1. Field of the Invention
The present invention relates to a method of removing nitric acid from an aqueous solution that allows selective separation of nitrate ion from an aqueous solution containing multiple components including nitrate ion and a method of producing drinks by using the same. In particular, the invention relates to a method of removing nitric acid from an aqueous solution that is applicable to and allows selective removal of nitrate ion from aqueous solutions containing vegetable-derived components such as vegetable extract and enables convenient and cost-effective production of nitric acid-free drinks and a method of producing drinks by using the same.
2. Related Art
Commercially available packaged vegetable juices, which are produced from vegetable extracts or purees, are highly recognized as health drinks because of their nutritional value, and have been consumed by a greater number of people after tastier vegetable juices were made available by improvement in blending and others. Juices are advantageous in convenience in taking nourishment, but if the juices are contaminated with some harmful component, that component is also taken probably in a large amount.
Nitrate ion is a component that is feared to be possibly involved in production of carcinogenic substances such as nitrous acid and nitrosoamine in the body, and ingestion of nitrate ion is undesirable for health. Accordingly, there is a regulation on the nitrate concentration in potable water. Among garden stuff, vegetables also contain nitrate ion, and there are some countries setting, for example, an allowable limit or a target value. Vegetable juices are possibly contaminated with the nitrate ion originating from vegetables, and it became necessary to prevent the ingestion of nitrate ion in a large amount due to ingestion of vegetable juice. Thus, it has been discussed whether it is necessary to establish a provision restricting the nitrate ion concentration contained in the drinks produced from vegetable extracts and purees, and the methods of reducing the nitrate ion in drink production are now under development.
The methods for preventing the nitric acid ingestion from vegetable juice possibly include a method of reducing the nitric acid value in raw vegetable during cultivation and a method of removing the nitric acid present in the extract obtained from vegetable; but the method of removing nitric acid from extract is preferable from the point of reliability of operation independent of the distributional or other circumstances of vegetable, and thus, it is desirable to establish such a method.
Use of an anion-exchange resin has been known as the method of removing nitrate ion. For example, in Document 1 below, vegetable extracts are processed with an anion-exchange resin after an organic acid is added thereto for a counter ion and bound to the inorganic anions. Alternatively in Document 2 below, nitric acid is removed from a carrot juice by using a strongly basic anion-exchange resin. Also in Document 3 below, vegetable extracts are treated with a strongly basic anion-exchange resin, and the anion-exchange resin is regenerated with an aqueous sodium hydroxide solution and then washed with an aqueous sodium chloride solution.
Yet alternatively, in Document 4 below, chlorine and nitric acid are reduced by treating an extract of green leaf of a rice plant with an OH-type anion-exchange resin.
Document 1: Japanese Patent Application Laid-Open No. 2000-354475
Document 2: Japanese Patent Application Laid-Open No. 59-31678
Document 3: Japanese Patent Application Laid-Open No. 11-290041
Document 4: Japanese Patent Application Laid-Open No. 5-7471
However, the methods of Documents 1, 3 and 4 demand a counter ion and raise the processing cost. Although it is unclear, a counter ion seems to be needed also in Document 2, similarly to other literatures. Moreover, in the cases of Documents 2 to 4, the anions in the liquid are replaced with chlorine or the liquid is demineralized, resulting in change in taste, and thus, it becomes necessary to adjust the taste once again after the treatment. In addition, all the methods in the Documents demand regeneration of the ion-exchange resin, resulting in increase of running cost, complication of the entire operation, and limitation for the period allocated for removal of nitric acid.